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audrey
09-16-2003, 09:19 AM
How do you dissolve a carbon steel tap from an Aluminumn Housing. A friend gave it to me to remove and its badly hacked up. The case is from a Harley and is highly Polished. I read in a guy lautard book many years ago about an acid that would eat away at the tap and leave the case alone. Do you know what type of acid it was? Was it Nitric Acid? Where would I get some of it? Any other tips on how to get the tap out would be appreciated. Thanks Audrey

JCHannum
09-16-2003, 09:26 AM
It was alum, available in supermarket in canning section. It is slow, and works best if heating is possible. (100-200* F)
Carbon steel can be heated to red and drilled out, or drilled out with carbide bit.

SGW
09-16-2003, 09:58 AM
Yes, it's nitric acid. Aluminum (most aluminum, anyway) is quite acid-resistant.
No idea where you'd get some; high school or college chemistry lab?

If I tried this stunt, I think I'd test the particular aluminum alloy I had to be sure it was indeed resistant to acid.

But the alum idea is probably easier.

Evan
09-16-2003, 12:25 PM
Audrey,

To easily dissolve a steel tap from an aluminum part put it in an anodizing bath. 1 part battery acid to one part water, always add acid to water, never water to acid when mixing. Use a sheet of aluminum as the cathode with aluminum wire and hang the part in the bath with aluminum wire. Connect a battery charger, negative to the aluminum sheet and positive to the part. Once again, all the metal in the bath must be aluminum (except the tap, of course). It is best to do this outside as it will evolve hydrogen gas and a slight acid mist. That tap will fizz like crazy and will be gone in a couple of hours, depending on size. You will need a good size bucket like a 5 gallon pail. The entire case should be submerged.

I don't advise messing with nitric acid. It is too nasty and it is hard to find. The above will work just fine, I've done it.


[This message has been edited by Evan (edited 09-16-2003).]

DR
09-16-2003, 01:23 PM
There is a product on the market, sold through tooling houses, that dissolves steel taps in aluminum. Ask at your local tool supplier.

Awhile back I used the stuff to remove sheared off bolts in an aluminum pressure washer housing. It never did completely eat the bolts, but enough to loosen them in the holes to pick out with tweezers.

Thrud
09-16-2003, 11:32 PM
audrey:
Try a Chemical supply house. You should not have any trouble getting it even up to carboys if you order it on your company letterhead and explain what you are using it for. I would ask for concentrated Nitric acid and not Red Fuming Nitric acid. Nitric acid will eat flesh much faster than other acids so make sure you have a hose handy for emergency washdown, use goggles and a facemask, and use rubber gloves.

I would try Evans method or the Alum first - much safer. If you can grind a flat on the top of the tap a carbide drill is much faster (or a LH drill).

Alternately hand it back to him and have him take it to an EDM shop.

pgmrdan
09-17-2003, 01:30 AM
.

[This message has been edited by pgmrdan (edited 03-08-2004).]

audrey
09-17-2003, 08:16 AM
Evan Your idea sounds great. Is it important to use a 2 amp 6 amp or 10 amp Charger as the Power Supply? Thanx again everyone for the Help. Audrey

Evan
09-17-2003, 12:33 PM
Audrey,

That is a pretty big piece of aluminum and will try to draw a lot of current. Use a 10 amp charger. If it trips the breaker reduce the size of the cathode sheet. I would start with the cathode sheet at about 6"x6". This should keep the current reasonable.

You can get away with one part acid to two parts water. It will be a bit slower.

When the part is done it will have a non sealed anodized coating. You should soak the part in cold water with a cup of bicarbonate of soda (Arm and Hammer) for a couple of hours to neutralize any acid. If you want to keep the anodized coating (it is clear) then boil the part for an hour in water. If you don't then soak it for 1/2 hour in a 5 gal pail of water with half a cup of lye mixed in to strip the anodic coating, soak again in plain water to rinse and buff the case shiny again. It will fizz like crazy in the lye but will only slighty matte the finish. Just don't forget it in the lye bath.

[This message has been edited by Evan (edited 09-17-2003).]

jfsmith
09-17-2003, 02:09 PM
Have you thought about putting it in the freezer and cause shrinkage and then use an extractor?

I think Crypto has a sheet of how and whys on getting broken taps out.


Jerry

Evan
09-17-2003, 03:09 PM
Jerry,

Aluminum shrinks twice as much as steel when cooled. Heating might be a better idea, boiling water would be about right.